The present invention relates to recordings of events concerning the terminals in a radiocommunication system. It relates more particularly to the method of activating such recordings.
The recording of certain events that can occur in a call or an exchange of information with a terminal is a routine operation in radiocommunication systems. The duly stored events are normally signaling messages, typically of level 3, interchanged between the terminal and the radiocommunication system. Such an operation is known by the term “trace”.
The trace is performed on one or more nodes of the radiocommunication system and can be used by the operator of this system for subsequent processing purposes (statistical analysis of calls in a geographic area, study of the behavior of a particular call, etc).
It has, for example, been the subject of standardization in the GSM (Global System for Mobile communications) system, in the technical specification TS 100 627 or GSM 12.08, version 4.6.1, “Subscriber and equipment trace”, published in October 2001 by the ETSI (European Telecommunications Standards Institute).
In the UMTS (Universal Mobile Telecommunication System) system, it is provided for the trace to be able to be implemented in the radio part of the universal terrestrial radio access network (UTRAN) to record signaling elements on the Iu interfaces (between a switch of the core network and a radio network controller), Iur interfaces (between two radio network controllers), Iub interfaces (between a radio network controller and a base station) and radio interfaces (between a radio network controller and a radio terminal).
The activation of the trace involves transmitting an instruction to the node which will carry out the recording. This activation is normally based on the identifier of a terminal for which calls need to be the subject of a trace. The identifier of the terminal can relate to the subscriber using the terminal. In this case, the identifier will advantageously be the conventional IMSI (International Mobile Station Identity) parameter. It may also relate to the terminal equipment. In this case, the identifier will, for example, be the conventional IMEI (International Mobile station Equipment Identity) parameter, a parameter obtained from the IMEI, or even the IMEISV (IMEI Software Version) parameter.
When the trace needs to be performed by a radio network controller in a system such as UMTS, that is, in an RNC (Radio Network Controller), two modes of activation are possible.
In a first mode, the trace is activated by the transmission of an instruction to the RNC from the core network. It is typically the HLR (Home Location Register), which is a database of the core network containing information relating to the subscribers of the network, which then originates the instruction, which will be transmitted to the RNC via the Iu interface. This mode of activation of the trace by signaling (signaling activation) is particularly suitable for performing a trace on calls from a particular subscriber of the network.
In a second mode, the trace is activated locally on the RNC. This activation is normally performed via an operation and maintenance center, for example, the OMC in UMTS which transmits the instruction to the RNC concerned. This mode of activation of the trace (management activation) is well suited in particular to the cases where there is a desire for recordings on a given area of the network, possibly for a particular type of equipment.
The second mode of activation is widely used in practice, particularly in the GSM system, because it is simple to implement and also provides operators with relevant statistics, for example concerning the behavior of a terminal model in a targeted geographic area of their network.
Transposing this functionality to the UMTS system would entail transmitting a terminal identifier to the RNC. Now, the main players in the field concerned consider the systematic presence of such an identifier within the RNC to be totally undesirable for various reasons.
Furthermore, when the terminal identifier used is an equipment identity, for example the IMEI, a trace activation at the RNC based on this parameter would require the RNC to be able to know the IMEI of each terminal involved in a call under its control. Normally, when an IMEI is transmitted by a terminal to the core network, it is done so transparently for the RNC. The RNC can therefore have the IMEI parameter only if the core network sends it to it specifically. Such a mechanism would then result in a signaling overload prejudicial to the system.